Oh, I forgot to include that in the list of idiosyncrasies. Basically, use setf wherever you would use = in Arc. The reason, in short, is that = is already the numerical-equality function, and CL doesn't like people to redefine things.
In PLT Scheme, you just have to uncheck a box that says "Disallow redefinition of initial bindings" and then you can redefine almost everything, but in CL, it will complain about breaking a package lock and go into the debugger whenever you try to redefine a built-in function, of which = is one. It's possible to tell it "Yes, ignore package lock", but I don't want to do that for every single function every time I start up SBCL. I think it is possible to tell it to automatically ignore the lock... But this is the way it is right now. Also, when you try to redefine 'if, you just run into a brick wall:
The special operator IF can't be redefined as a macro.
I stumbled on one other workaround, too... you can create a new package and choose not to import (all of) the stuff from CL-USER. So far, though, this doesn't even import the symbol nil, and when I do import it, it gets printed with a "COMMON-LISP:" prefix.
I guess one might be able to get used to that. Might try it out if I feel adventurous. For now, put up with using setf, mapcar, iff, and my version of with.
